Air Traffic Management: Next Phase

Airservices Australia has been a global pioneer in the use of automatic dependent surveillance-broadcast (ADS-B) for more than a decade. But while few other countries have kept pace in terms of deployment or application, the rapid rate of technological advance means Airservices is already looking to the next evolution in air traffic control surveillance.

The air navigation service provider (ANSP) operates a network of ground-based ADS-B stations that has given it continent-wide coverage at higher altitudes since 2012. However, a new system under development in the U.S. promises to eliminate the need for a ground network by relying on satellites instead, which would extend coverage to oceanic airspace and allow greater coverage at lower altitudes.

Airservices wants to be one of the users of the system after developer Aireon brings it fully online around 2019. This aim is influencing decisions on whether to upgrade the current terrestrial-based ADS-B equipment and also highlights the need to replace a backbone air traffic management (ATM) operating system with one better able to handle the increased surveillance data.

For many years, Australia could lay claim to having the most extensive ADS-B surveillance network. Now some others-including the U.S. –have also deployed ADS-B networks covering vast areas. Australia still has the largest network where ADS-B is the sole surveillance source, since unlike many countries, it has very little radar coverage of its interior.

Australia has also taken the most strides in requiring aircraft to be equipped with ADS-B compatible avionics. Key mandates include one in 2013 requiring aircraft above 29,000 ft. (Flight Level 290, or FL 290) to be equipped and another, last February, applying to almost all aircraft operating under instrument flight rules in controlled airspace.

Airservices has gradually built up its ADS-B network to 72 ground stations, which receive signals from aircraft based on GPS location. Coverage is virtually complete at FL 290, but diminishes progressively down to ground level.

Radar only covers a “J” shaped area on Australia’s heavily populated eastern and southeastern coasts, as well as smaller areas on the west and north coasts. This means ADS-B has allowed the advantages of air traffic control surveillance to be extended much further, as it is far cheaper and easier to install. Along with safety benefits, the broader coverage means separation can be reduced and aircraft can have greater routing flexibility.

The advantages have increased as aircraft equipage rates have risen.For example, reduced separation can be applied when both aircraft involved are equipped. Now virtually all aircraft operating in controlled airspace are ADS-B compliant. There are some exemptions through 2020, for private operators and foreign airlines in certain airspace, but these are applied to very few aircraft.

ADS-B has also allowed greater use of flight-planning options such as user-preferred routing and flex tracks for domestic and long-haul flights. This is because controllers have a more accurate picture of an aircraft’s position, altitude and heading.

Airservices is still expanding the ground-based ADS-B network and plans to deploy up to 15 more stations. These additional sites are intended to increase low altitude coverage in some cases, and in other places they will replace radars reaching the ends of their lives.

In a space-based ADS-B system, the satellites fulfill the role of the ground stations. Aircraft equipage would be the same as for the current ground-based ADS-B network.

If the new system eventually proves itself, Airservices would probably look to retire some of its ground-based ADS-B stations. Space-based ADS-B will probably be cheaper, and many of the original terrestrial stations will otherwise soon need upgrading with second generation equipment.

Airservices will still maintain at least a skeleton network of ground-based ADS-B as a backup, in much the same way it still retains ground-based navigation aids as a backup to GPS navigation.

However, many steps remain before Airservices can contemplate using space-based ADS-B. The company would essentially need to subscribe to surveillance data from Aireon, the U.S. based joint venture that is deploying the system. Iridium Communications and Nav Canada are the major stakeholders, along with a handful of European ANSPs.

Aireon will rely on a constellation of 66 satellites being progressively launched by Iridium. The first 30 have been sent into orbit in three launches, with the most recent on Oct. 9. The remainders are due to be launched by mid-2018. Aireon is already receiving aircraft positional data, which is being used for testing. Nav Canada is expected to be the first to use the service operationally by late 2018 or early 2019.

The Aireon system will be able to provide surveillance anywhere on the globe, and about 10 ANSPs have entered into surveillance data contracts. More than 20 others, including Airservices, have signed agreements to evaluate the service in their regions.

Airservices hopes to have an initial contract in place by early next year to at least begin receiving some data, which will allow it to start building a safety case for Australian regulators. Operational use by Airservices is unlikely to occur before 2020, however, as the safety and cost-benefit assessments will require a lot of work. No cost estimate is available yet.

The fact that Australia already have a mature ADS-B network will make it easier to validate the Aireon service. When it has been proven to be as accurate as the existing system, it will be a matter of providing the right interface to feed the new data into Airservices control rooms.

While many others are interested in Aireon’s system, it will be particularly well-suited to Australian requirements. Airservices control 11% of the world’s airspace, most of which is oceanic and out of range of current surveillance technology. “This would be a fantastic enhancement for us” he says.

Aireon views Australia as an important potential addition to its network, says Cyriel Kronenburg, the company’s vice president for aviation services. Airservices is “a true pioneer of ADS-B and is already reaping the benefits of a terrestrial-based system. “We see our technology as the next logical step” for surveillance over the enormous area Airservices covers,” he notes. “To be able to collaborate on the deployment of space-based ADS-B in Australian airspace would be in an incredible opportunity for Aireon to really hone in on separation capabilities and efficiency-enhancing services and processes.”

While some countries regard space-based ADS-B as primarily a solution for oceanic surveillance, Airservices is looking at it for domestic coverage, too, Angus says. Aircraft coming in on international routes can sometimes be over Australia for 3-4 hr. before reaching the east coast cities. Airservices uses the same platform to monitor flights, whether they are over land or sea.

The current ADS-B system relies on line of sight between ground stations and aircraft, so the coverage area from each land-based site is an inverted cone that shrinks closer to the surface. Space-based ADS-B, however, offers full coverage down to ground level. This means it will provide far more complete low-level surveillance than the terrestrial system.

In the oceanic environment, the Aireon surveillance will allow the same hands-on air traffic control and separation standards as over land. Airservices’ terrestrial network only extends a limited distance offshore, although it has extended coverage into the Tasman Sea with an ADS-B site on Lord Howe Island.

There is currently a coverage gap on the busy air routes between Australia and New Zealand. However, ANSP Airways New Zealand is also evaluating Aireon’s system, so there could eventually be full coverage between the two countries, Harfield notes. While these are relatively short flights, the sheer volume of traffic means any greater efficiency could result in significant savings for airlines. There would even be the potential for controlling traffic all the way across the Tasman from either side.

The introduction of space-based ADS-B would dramatically increase the flow of surveillance data. This means Airservices will have to upgrade its air traffic control operating system to integrate the additional feed, says Harfield.

While some of the space-based ADS-B data could be handled by the current ATC system, it would not be able to process all of the extra load. So Airservices will not get the full benefits of Aireon surveillance until it installs its planned ATC system replacement, under a project known as OneSky. This will partly determine the timing of space-based ADS-B implementation.

OneSky aims to deploy a common ATC system for both Airservices and Australia’s Department of Defense. It will make the system more flexible, scalable and will have more tools for controllers. Airservices selected Thales as the main supplier in 2015, and a full contract for OneSky is expected to be signed before the end of this year. Some preparatory development work is already underway.

Airservices now estimates that the OneSky deployment will be completed by 2023, later than its initial forecast of 2021. However, Harfield notes this is conservative, and he predicts the actual completion date could be closer to 2022. Airservices expects to spend A$652 million ($510 million) on OneSky and its enabling projects over the next five years.

The OneSky system will be deployed at 12 military and four civil ATC centers. It is expected to be operational at the first sites around 2020 and then be progressively rolled out at the others.

Space-based ADS-B is also linked to another new technology Airservices intends to introduce. It plans to install a long-range air traffic flow-management system in order to better coordinate international arrivals at the major Australian gateway airports.

Airservices already has a flow-management system that it uses for domestic flights, which is particularly helpful in using ground-delay programs to optimize traffic flows during severe weather. However, because international long-haul arrivals are less predictable, they can disrupt carefully planned patterns.

A long-range flow-management system would allow Airservices to better integrate international traffic with domestic flows. International flights could be directed to alter their speeds slightly in order to meet an optimal arrival time. Space-based ADS-B would vastly improve such a system, Angus says. Aircraft trajectories can be more precisely managed if controllers know an aircraft’s location during long-distance oceanic flights.

A request for information was issued to see what long-range flow-management solutions could be offered by potential suppliers, says Airservices Chief Information Officer Chris Seller. This yielded response from about 15 companies, and these are now being assessed. The intention is to launch a trial, which will probably be conducted at Melbourne International Airport, he says.

The moved toward satellite-based technology is evident in other areas aside from ADS-B. For example, Airservices has also installed ground-based augmentation systems (GBAS) to provide precision runway approaches at Sydney and Melbourne airports. GBAS is regarded as an alternative for the more traditional instrument landing systems (ILS). It is more accurate and cost effective through its use of enhanced GPS data. Airservices is considering using GBAS to replace its legacy ILS systems when they are due to be retired, and it could also be installed in lieu of ILS when a new runway is completed in Perth.

Another satellite navigation technology under development offers potential benefits for aviation in Australia. Government agency Geoscience Australia has launched a two-year trial program for a satellite-based augmentation system (SBAS), which is intended to improve the accuracy of GPS for positioning in multiple applications. Other government agencies are also involved, and Airservices will probably evaluate the use of SBAS for precision approaches to regional airports, Harfield says. In the long-term, it could also help improve aircraft navigation in remote areas.

The technical advances planned by Airservices will follow a major corporate restructuring at the organization, including a substantial reduction in headquarters staff. Together, the restructuring and the new systems represent a significant change in how Airservices will provide air traffic control in Australia. This transformation is an example of how throughout the aviation industry, “old business models are dying and new ones are emerging.

Source: AW&ST October 16-29, 2017

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